1. Field of the Invention
The invention is directed to a ballast system for a flourescent lighting system and more particularly to a high frequency transistorized ballast.
2. Description of the Prior Art
It was recognized early in the development of flourescent lighting that efficiency increases with increasing operating frequency. During the 1960's, some attempts were made to utilize this increased efficiency coupled with solid-state high frequency inverters. However, the solid-state devices available at that time were expensive and had marginal characteristics for the application involved.
In the past two years, the state of the art relative high voltage semiconductors has become practical and inexpensive. Therefore, it is now feasible through careful design to produce a more efficient flourescent lighting system at a competitive cost.
U.S. Pat. No. 3,579,026 discloses a rectifier circuit with a switching circuit built thereinto. U.S. Pat. No. 3,710,177 discloses an inverter that supplies voltage at a frequency less than the resonant frequency and the improvement therein is the use of a means within the inverter whereby the inverter can deliver a reduced voltage at a frequency near the resonant frequency to facilitate conditioning of a lamp. U.S. Pat. No. 3,758,821 discloses the use of a saturated coil transformer having magnetic properties such as to cause an increase in the frequency of the oscillator as the load on the output transformer increases. Finally, U.S. Pat. No. 2,928,994 discloses a lamp ballast wherein there are frequency variations proportional to the voltage of the source and induction in the lamp circuit will compensate for frequency variations to maintain substantially constant lamp current.
Transistorized inverters have been taught in the EEE magazine as far back as February 1969 (pages 114-116) and in the Electrical Manufacturing magazine as far back as the January--February 1960 issue (pages 79-94).
There exist in the art many patents which are directed to transistor ballast systems for flourescent light circuits. Typical of these patents are U.S. Pat. Nos. 3,769,545; 3,766,467; 3,754,160; 3,700,956; and 2,964,676. All of these patents disclose different transistorized circuits for driving flourescent lamps.